The present invention relates to a flexible, tear resistant composite sheet material and a method for producing the same. More specifically, it relates to composite sheet material made from a nonwoven web of thermoplastic microfibers containing a plurality of staple fibers which are subjected to sufficient heat and pressure to at least soften the microfibers so that they can be formed into a contiguous staple reinforced sheet having certain definable properties which make the composite sheet material suitable for a number of high strength uses including abrasive backing materials, tapes, furniture fabric, interliner for clothing, geotextiles and belt material for conveyor machinery and the like.
Abrasive backing materials, adhesive tapes and geotextiles are but a few examples of materials which are formed from flexible substrates which have been further treated or converted to permit their use in high strength and tear resistant applications. Abrasive materials such as sandpaper, sanding pads and sanding belts are typically made from paper or fabric and then further treated with such materials as latexes, resins and other saturants and additives to improve their strength, tear resistance and useful life. These materials while having been greatly improved over the years, still suffer from deficiencies in overall strength and tear resistance as well as cost. Abrasive backing materials made from paper are economical to produce but suffer from the standpoint of strength, tear resistance and useful life. Fabric-backed abrasive materials provide a marked improvement over paper-based materials in the areas of strength, tear resistance and useful life, but such improvements come at the expense of significantly higher material and production costs. Furthermore, despite their improvements over paper-based products, such fabric-backed abrasive materials still lack sufficient strength and tear resistance for certain applications. As a result, there is a need for a high strength, low cost, tear resistant material.
In the areas of tapes, the needs and problems are similar to those found with abrasive backing materials. Tapes in varying applications require materials which are, among other things, flexible, waterproof, strong in the machine and cross-directions and which readily accept adhesives while being able to release from themselves. Consequently, there is a concurrent need for a high strength, tear resistant material which can be used in the construction of tapes.
Geotextile materials are permeable high-strength fabrics which are used to prevent soils from migrating into drainage systems, allow water to migrate into drainage systems, prevent erosion damage, and serve as a separator between soil and road base materials. There is a wide range of product applications and the strength requirements vary for each application. The two main properties of geotextiles are permeability and strength. The Federal Highway Administration has established physical strength categories for light, heavy, and severe product applications. The drainage and erosion product applications are in the light-heavy and heavy-severe categories, respectively. The flexible tear resistant composite sheet material of the present invention has the design capabilities to serve all three physical strength categories. This is accomplished with the high tear resistant, puncture-proof, and burst strength properties of the present invention. The ability to control the void volume enables the composite sheet material to have a range of permeabilities. Also, the range of permeabilities can be controlled by varying the staple to microfiber ratio and staple fiber diameter. The temperature stability of the sheet composite can be designed for low temperature drainage or high temperature roadway applications.
The present invention provides a material which is suitable for the above uses as well as a number of other uses or applications which require a material with similar properties. The scope of this invention should therefore not be restricted to above applications. The advantage of the present invention resides in its ability to provide a high strength, low cost, tear resistant material which is flexible, yet porous and readily accepts further treatment and/or conversion as in the case of abrasive backing material, adhesive tape and geotextile applications. In addition, the material of the present invention may be formed or molded into flexible three-dimensional shapes for nonplanar applications. These and other objects and advantages of the present invention will become more apparent from a further review of the following specification, drawings and claims.